The Socialist government is trying to forge its fiscal credibility with a 2013 budget which relies on forecasts that Europe's second-biggest economy will grow 0.8 percent next year after an estimated 0.3-percent expansion this year.

However, private-sector economists widely expect lower growth next year. The International Monetary Fund forecast on Monday the economy would grow only 0.1 percent this year and 0.4 percent in 2013, cutting its estimates from 0.3 percent and 0.8 percent respectively in July.

"We are just discussing our budget in the (National) Assembly and our prospects, our forecast, for growth are ... realistic," Moscovici told journalists on the sidelines of an EU finance ministers meeting in Luxembourg.

Moscovici has insisted the government has enough political will to stick to its deficit reduction targets even in the face of growing doubts about its economic outlook.

The government, which has pledged to cut the public deficit to 3.0 percent of economic output in 2013 from 4.5 percent this year, will have little choice but to raise taxes or make painful spending cuts if growth falls short of its forecast next year.

The 2013 budget is already France's toughest in at least three decades with 10 billion euros ($13 billion) in tax hikes for the wealthy and another 10 billion euros in tax hikes affecting businesses.

Five months into office, President Francois Hollande's approval ratings are falling in the face of high unemployment and growing dissatisfaction with the government's austerity drive.

On Tuesday, thousands of protesters took to the streets in major French cities, in marches against austerity called by the hardline CGT union.